The tongue is a complex muscular organ that is critical for oro-motor behaviors such as swallowing, breathing, speaking and chewing. The astonishing complexity and precision of the voluntary movements performed by the tongue depend upon the coordination of intrinsic (origin and insertion within the body of the tongue) and extrinsic (attached to bone and inserted into the base of tongue) tongue muscles. Until recently, almost all studies of lingual muscle function whether in speech, respiration or deglutition have concerned themselves with the study of whole muscle electromyographic (EMG) activities. Recently, we characterized respiratory-related tongue muscle and motor unit activities in healthy human subjects as a function of sleep/wake and in slow volitional movements. The results of this work provided de novo insights into lingual motor function and a platform from which to begin studies aimed at identifying how tongue muscles are controlled in more complex volitional behaviors. The current application builds thematically on previous work by the PI and yet departs from previous investigations in incorporating critical elements of the speech production process. Specifically, we propose to examine tongue muscle and motor unit activities and the potential for these activities to be modulated by inputs arising in the respiratory, phonatory (laryngeal) and/or supralaryngeal (oral- articulatory) subsystems. Understanding muscle and MU activities as a function of these influences separately and when successively overlaid is a logical first-step toward understanding how tongue muscle and motor unit activities are modulated in the more complex volitional behavior that is human speech production.